This statement is clearly given from what we might call a globalist perspective. The author of this statement clearly believes that nationalism is a harmful influence and should be eradicated if possible.
Nationalism is the idea that your particular nation is in some way special and is better than other nations in significant ways. From a nationalist perspective, you are a citizen of your particular country first, not a "citizen of the world." Therefore, you should prefer your country to other countries and should work to make your country stronger, not caring about what happens to other countries.